Even in the case of rotating an impeller having at least one impeller blade as shown in FIGS. 1A and 1B, a lift side and an opposite lift side are cancelled by each other, and of course, the lift cannot be generated in view of common sense and of a theoretical sense. Accordingly, there has been considered a method of reducing wind pressure during a period that the blade rotates in the opposite lift side. For example, there is a method of letting out the wind pressure by arranging a valve, a method of changing a direction against the wind pressure, a method of reducing an area, and the like. Each of these methods has a complex structure, tends to generate a trouble, accompanies a vibration and noise, and has a deteriorated efficiency. Accordingly, aircraft utilizing such impeller have not been put to practical used as the matter stands. As mentioned above, in conventional, there is a defect that the lift cannot be generated without using a valve, an eccentric cam and the other complex mechanisms.